This invention relates to an automatic document feeder in an image reading apparatus. More particularly, this invention relates to an original transport path for automatically feeding an original to an image reading position, for aligning pages of the originals that are read, and for discharging the originals.
In a conventional automatic document feeder used in an image reading apparatus such as a copier, a facsimile and an image scanner, it is well known that a device such as one disclosed in Japanese Patent Publication (Tokkai) No. 07-175279 can read both sides of an original.
In Japanese Patent Publication (Tokkai) No. 07-175279, it is described that the originals are fed from a sheet supply tray along an original supply path toward a reading portion facing a reading device on an image reading apparatus. After reading one side of the original by the reading device at the reading portion, the original is switched back via a switchback path that uses a space established between a sheet supply tray and a discharge tray, and is re-fed from the original supply path to the reading portion to read a back side of the original. Then, the original, whose front and back sides have been read, enters the switchback path again to switch back the front and back sides to change a page order for discharging, and is subsequently discharged to the discharge tray via the reading portion.
However, this automatic document feeder requires the original to pass through the reading portion three times to read both sides thereof, making the process of reading a two-sided document inefficient and taking a longer time to process such an original.
In order to solve the problems, in a system disclosed in Japanese Patent Publication (Tokkai) No. 10-81449, the original is fed from a sheet supply tray and is supplied along an original supply path formed of a large transport roller to an original reading portion facing a reading device on an image reading apparatus. After reading one side of the original by the reading device at the reading portion, the original is switched back via a switchback path formed below a discharge tray. While sending the original to the reading portion from the original supply path again, the backside of the original is read. Further, the original, whose front side and backside have been read, enters the switchback path to switch back the front and back sides to change a page order for discharging, and is subsequently discharged to the discharge tray. The front side and backside of the original are inverted in an inverting discharge path directly connected between the switchback path and the discharge outlet.
According to this automatic document feeder, because the path is formed to invert the original and change the page order of the originals without passing through the reading portion, the double-sided original needs to pass through the reading portion only twice upon reading. Therefore, it is possible for the next original to be supplied directly after reading the backside of the previous original, so the time for processing the original is shortened.
However, in such an apparatus, the switchback path needs to have a length long enough to accommodate the maximum length of the original in addition to a length of overrun for stopping and driving the original, so the apparatus tends to become large.
Furthermore, when advancing in the switchback path, only a trailing edge of the original is nipped in an advancement direction to be inverted. Therefore, a large-sized original with a deformed portion due to curling or being folded touches a guide in the switchback path when advancing, thereby making it difficult to transport such an original smoothly, resulting in a paper jam.
In view of the aforementioned problems, an object of the present invention is to provide an efficient and compact apparatus for securely transporting and feeding the original.
In order to attain the aforementioned object, this invention is provided with a plurality of switchback paths at downstream of a reading platen to turn over an original in the transport direction. A recognition device determines a length of the original guided toward the reading position. According to the length of the original, one of aforementioned switchback paths is selected, and the original is guided into the selected switchback path. Therefore, the original can be fed into an appropriate switchback path, in consideration of smooth original transport and efficient processing.
As another embodiment of the invention, an apparatus is provided with the first switchback path utilizing a space between a sheet supply tray and a storage tray arranged to overlap, and the second switchback path arranged between the storage tray and a platen. One of the first and second switchback paths is selected, and the original is guided therein. Thus, the apparatus cab be made compact, does not cause erroneous transport, improves the processing efficiency, and feeds the original to the appropriate switchback path.